z=$(($z+3))
z=$((z+3)) # Also correct.
# Within double parentheses,
#+ parameter dereferencing
#+ is optional.
# $((EXPRESSION)) is arithmetic expansion. # Not to be confused with
#+ command substitution.
# You may also use operations within double parentheses without assignment.
n=0
echo "n = $n" # n = 0
(( n += 1 )) # Increment.
# (( $n += 1 )) is incorrect!
echo "n = $n" # n = 1
let z=z+3
let "z += 3" # Quotes permit the use of spaces in variable assignment.
# The 'let' operator actually performs arithmetic evaluation,
#+ rather than expansion. |